In the universe of "House of the Dragon." it has been mentioned several times that among the Targaryens, there were those called "Dreamers" who had the power of prophecy. Aegon the Conqueror was among them and Haelena Targaryen is now canonically a Dreamer as well.
Aemond Losing His Eye
As Helaena was examining a millipede while her mother, Alicent Hightower was around, she uttered some bizarre words that would sound random to anyone who heard them. Even Alicent thought nothing of it, but if you listen, she had predicted Aemond's tragic loss.
"He'll have to close an eye," she said. She was, of course, referring to Aemond losing his eye after Lucerys Velaryon slashed him with a knife in defense of his brother. This led to one of the most intense scenes in the show so far, wherein he said it was fair since he gained a dragon anyway.
Viserys' Blinding Love for Rhaenyra
During the same scene with young Helaena, she also said: "It has eyes, though I don't believe it can see." It was easy to assume that she was referring to the millipede she was holding, but she was actually talking about her father, King Viserys Targaryen.
While it can mean many things, the situation that fits it best is Viserys' loyalty to his first child, so much so that he overlooks the obvious fact that her first three sons were not of Laenor Velaryon, but of Ser Harwin Strong as shown evident by the color of their hair.
Princess Rhaenys and Meleys Arriving at the Coronation
During another scene where a distressed Helaena was conversing with her mother, she said "There is a beast beneath the boards." Alicent, thinking she was just odd, replied "Oh, my dearest love," not putting any weight to her words.
Many fans believe that she was predicting Princess Rhaenys Targaryen and Meleys arriving in epic fashion during the coronation of Aegon II Targaryen, where she broke through the Grand Sept and made everyone fear for their lives.
The Plot to Usurp the Throne
As young Helaena is once again examining one of her bugs, a spider this time, she once again relayed another prophecy. "Hand turns loom, spools of green, spools of black, dragons of flesh weaving dragons of thread."
This may be in reference to Alicent putting his son on the throne after misunderstanding Viserys' delusional ranting. Although she mentioned "Hand turns loom," speaking about the Hand, Otto Hightower, who has been plotting to put his kin on the throne since Alicent was just a young girl.
Jaehaerys' Death
In the first episode of the second season, she told Aegon that she was afraid, to which Aegon responded that she shouldn't be since Vhagar, the largest dragon alive, is protecting the city. She clarified what she meant and said "Not the dragons. The rats."
Seeing as Jaehaerys was killed soon after, we can safely assume that she was referring to Blood and Cheese, or the mercenary and the rat catcher that Daemon hired to kill Aemond Targaryen but instead went for Aegon's son.
